JPH0459049A - Catalyst for diesel engine exhaust gas cleanup - Google Patents

Abstract

PURPOSE:To obtain a catalyst capable of efficiently removing particulate substances in exhaust gas by providing a catalyst components consisting of inorganic oxide, noble metal, and rhodium and incorporating rhodium only into the upper layer part of a catalyst component holding layer. CONSTITUTION:Catalyst components containing refractory inorganic oxide, such as alumina and silica, palladium and/or platinum, and rhodium are held by a refractory three-dimensional structure, such as ceramic foam, and this rhodium is incorporated only into the upper layer part having a thickness equivalent to <=80% of the thickness of the catalyst component holding layer. The resulting catalyst for engine cleanup is excellent in the property of combustive removal of harmful components, such as unburnt hydrocanbon and carbon monoxide, other than carbonaceous particulates from low temp. and is reduced in the oxidizing power of sulfur dioxide.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a catalyst for purifying diesel engine exhaust gas.

(Prior Art) In recent years, particulate matter particularly in diesel engine exhaust gas mainly consists of solid carbon particles, sulfur-based particles such as sulfates, liquid or solid polymer hydrocarbon particles, etc. These are collectively referred to as ``fine particulate matter'') and environmental health. The reason is,
This is because these particulate substances have particle diameters of approximately 1 micron or less, and therefore are easily suspended in the atmosphere and easily taken into the human body through breathing. Therefore, studies are underway to tighten regulations regarding the emission of these particulate matter from diesel engines.

On the other hand, improvements such as increasing the pressure of the fuel jets of diesel engines and controlling the timing of the fuel jets have reduced the amount of particulate matter emitted from diesel engines to some extent. However, the reduction has not been sufficient, and organic solvent soluble components (SOF), which mainly consist of liquid high molecular weight hydrocarbons, are contained in particulate matter.
Improvements in engines such as those described in Section 2 have resulted in an increase in the proportion of SOF in particulate matter.
Therefore, removal of SOF along with particulate matter has become an important issue.

Ceramic foam,
Catalysts supported on combustible three-dimensional structures such as wire mesh, metal foam, graded ceramic honeycombs, open flow type ceramic honeycombs, and metal honeycombs, which are capable of burning carbon-based fine particles. is used to capture particulate matter in the diesel engine exhaust gas, and under the exhaust gas emission conditions (gas composition and temperature) obtained under normal day-cell engine running conditions, or by means of heating such as an electric heater. A catalytic method for removing carbon-based particulates using carbon dioxide has been investigated.

In general, catalysts for purifying exhaust gas from day-cell engines have the following characteristics: (a) high efficiency in combustion removal of harmful components such as carbon-based particulates, unburned hydrocarbons, and carbon oxides from low temperatures; It has a low ability to oxidize diacid (Hisulfur C3O2), which is generated from the sulfur component contained in a large amount in light oil used as a gas oil, to sulfur trioxide (SO3).
(3) It has the ability to suppress the formation of sulfur dioxide (oxidized to sulfur trioxide and sulfuric acid), and (3) it has the ability to withstand continuous operation under high loads, so-called high temperature durability. Catalysts are desired.

Conventionally, various proposals have been made for the purpose of increasing the combustion removal efficiency of carbon-based particulates.

For example, JP-A-55-24!397 discloses that platinum group element catalysts include rhodium (7.5%) platinum alloy, platinum/palladium (50/50) mixture, tantalum oxide, or cerium oxide. Also disclosed are alloys containing palladium and 75% by weight or less of platinum. These catalysts are also SOF
It is also said to be effective in removing.

In addition, JP-A-61-129030, JP-A No. 61-14.
9222 and 61-146314,
A catalyst composition containing palladium and rhodium as the main active ingredients, with the addition of alkali metals, alkaline earth metals, copper, lanthanum, zinc, mankan, etc. is also disclosed in JP-A-59-82944. , alkali metals, molybdenum, and vanadium and at least one selected from platinum, rhodium, and palladium are disclosed.

An oven-type honeycomb-shaped noble metal oxidation catalyst having through holes parallel to the gas flow has been reported as a catalyst for removing SOF from diesel engine exhaust gas (SA, E Paper, 810263).

(Problem to be solved by the invention) However, although the above-mentioned conventional catalysts are all effective to some extent in the combustion removal of Hagi-based fine particles or the removal of SOF, they have a high ability to oxidize sulfur dioxide. The production amount of sulfate increases, and the overall removal rate of particulate matter decreases, and this sulfate also poses a new environmental problem.

In other words, the performance required for the catalyst for purifying diesel carrot exhaust gas in (a) to (c) above, roughly speaking, the SOF
A catalyst with sufficient removal performance? i have not been found.

Therefore, one object of the present invention is to provide a catalyst for purifying diesel engine 11 gas that can efficiently remove particulate matter from diesel carrot exhaust gas.

Another object of the present invention is to have the ability to burn off harmful components such as unburned hydrocarbons and carbon oxides in addition to carbon-based particulates in diesel engine exhaust gas at low temperatures, and to have a low oxidizing ability for sulfur dioxide. An object of the present invention is to provide a catalyst for purifying a diesel engine that suppresses the generation of sulfate.

Another object of the present invention is to reduce the amount of S in diesel engine exhaust gas.
An object of the present invention is to provide a catalyst for purifying diesel exhaust gas that can efficiently remove OF.

Another object of the present invention is to provide a day-cell engine purifying catalyst that can be installed in a diesel vehicle without causing problems such as high temperature durability, good after-effects, and practical use.

(Means for Solving the Problems) The inventors have made extensive efforts to achieve the objects stated in section 2.
As a result, (a) 1rtiJ flammable inorganic oxide,
(1)) palladium and/or platinum, and (c
) A catalyst in which a catalyst component containing rhodium is supported on a refractory three-dimensional structure, which selectively contains rhodium in the upper layer of the catalyst component support layer, or in addition to carbon-based fine particles, unburned hydrocarbons, - It has excellent performance in burning and removing harmful components such as carbon oxide at low temperatures, and has a low ability to oxidize sulfur dioxide.
Furthermore, they found that it is effective in removing SOF, and based on this knowledge, they completed the present invention.

That is, the present invention provides (a) a refractory N-free oxide, (l
]) A catalyst for diesel engine exhaust gas purification in which a fire-resistant three-dimensional structure supports a catalyst component containing at least one noble metal selected from palladium and platinum, and (c) rhodium, the catalyst component supporting layer having a thickness of Sano 80
The present invention relates to a catalyst for purifying diesel engine exhaust gas, characterized in that rhodium is contained only in the upper layer portion with a thickness corresponding to % or less.

The present invention will be explained in detail below.

As the refractory inorganic oxide (a), activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, zeolite, etc. are used. Zirconia can be cited as a suitable base material that suppresses the formation of sulfate and exhibits excellent selective oxidation ability.

As the starting material for platinum, which is component (b), chloroplatinic acid, dinitrodiaminoplatinum, platinum tetramine chloride, platinum sulfite complex salts, etc. can be used.

In addition, starting materials for palladium include palladium nitrate, palladium chloride, balacillano, tetramink IJ light, and palladium sulfite salt.

Examples of the starting material for rhodium as component (c) include rhodium nitrate, J\xaammine rhodium chloride, and rhodium sulfi I-complex salt.

Further, as the refractory three-dimensional structure, ceramic foam, ceramic honeycomb of one orb rough type, wall flow type honeycomb monolith, open flow metal honeycomb, metal foam, metal mesh, etc. can be used.

In particular, if the diesel engine exhaust gas contains 100 mg or less of particulate matter per 1 hour of exhaust gas, and the SOF content in this particulate matter is 20% or more,
As the flammable three-dimensional υ4 structure, open flow type ceramic honeycomb or metal honeycomb is suitably used.

The catalyst of the present invention has a catalyst component containing the components (a) to (c) listed above supported on the above-mentioned refractory three-dimensional structure, and has a thickness of 80% or less of the thickness of the catalyst component supporting layer. It is characterized in that rhodium is contained only in the layer portion with a thickness corresponding to 0% (excluding 0% where no rhodium is present). That is, in the catalyst of the present invention, rhodium is larger than 80% of the thickness of the catalyst component support layer in the thickness direction from the surface of the catalyst component support layer.
% or less is contained only in the upper layer portion.

As mentioned above, there is no particular restriction on the method of containing rhodium only in the upper layer of the catalyst component supporting layer, and examples include the following.

That is, refractory inorganic oxide (a) and platinum and/or
Alternatively, a catalyst component containing palladium (1) is supported on a refractory three-dimensional structure to form a first layer, and then a catalyst component containing a refractory inorganic oxide (a) and rhodium (c) is formed. The second layer is formed by supporting IT radium C on the first layer.
) is formed.

” 2. In the second layer, platinum and/or rose silano,
Platinum and/or palladium (b) may be included in the first layer and rhodium (c) in the second layer.
) is the most effective way to use precious metals.

The catalyst of the present invention comprises the above refractory n-free oxide (a), platinum and/or palladium (1)) and rhodium (c).
Besides! It may contain at least one element selected from rare earth elements such as lanthanum, cerium, praseodymium, neodymium, and monomarium.

In the catalyst of the present invention, the amount of the refractory inorganic oxide (a), platinum and/or palladium (1), and rhodium (c) constituting the catalyst component support layer is determined by the amount of the refractory three-dimensional structure. 3 to 300g per 1g, thicker than 0 and 6g or less, thicker than 0 and 3g or less, and 0.01 to
It is preferable that the amount is in the range of 1 g.

The amount of the rare earth element added as necessary is preferably in the range of 1 to 5 g per 1 g of the refractory three-dimensional structure.

As mentioned above, in the catalyst of the present invention, SiL, Rhodium (
c) is contained as an essential component, and this rhodium (
c) It is necessary that the upper layer portion containing rhodium (
c) or not, or even if it does, the upper layer containing it or the entire catalyst component carrier 1. ．． If the thickness exceeds 80% of the thickness of layer j, the ability to remove particulate matter will decrease, making it impossible to achieve the object of the present invention.

There are no particular restrictions on the method for preparing the catalyst of the present invention.
Specific examples are as follows.

(1) A refractory inorganic oxide powder is wet-pulverized into a slurry, a refractory three-dimensional structure is immersed in this slurry,
After removing excess slurry, it is dried at 80-250°C, and then heated at 300-850°C.

Next, the above refractory three-dimensional structure is immersed in an aqueous solution containing a sium compound of a predetermined f('z) to adsorb and support the rhodium compound, and then the excess solution is removed and the 80-2
Dry at 50°C and then bake at 300-850°C.

Finally, the refractory three-dimensional structure is immersed in an aqueous solution containing a predetermined amount of platinum and/or palladium compounds - after removing excess M i'f
The catalyst is dried at C and then calcined at 300 to 850 C to obtain the desired catalyst.

(2) The 1Tli'l refractory three-dimensional structure is immersed in a slurry containing a platinum and/or palladium compound and a refractory inorganic oxide, and after removing excess slurry, the temperature is 80 to 250°C. +2 drying, then 300~
The first layer is formed by firing at 800°C.

Next, the refractory three-dimensional structure with the first layer formed thereon is immersed in a slurry containing a rhodium compound and a refractory 11I+' organic oxide, and after removing excess slurry,
It is dried at 80-250°C and then calcined at 300-800°C to form a second layer to obtain the desired catalyst.

(Effects of the Invention) The catalyst of the present invention has excellent performance in removing harmful components such as carbon-based fine particles, unburned hydrocarbons, and carbon oxides from low temperatures, and has a low ability to oxidize sulfur dioxide. Therefore, it is possible to suppress the production of Zarphae). Therefore,
The catalyst of the present invention is excellent in reducing particulate matter in diesel engine exhaust gas, and by using the catalyst of the present invention, diesel engine exhaust gas can be efficiently purified.

Since the catalyst of the present invention has excellent SOF removal ability, it is extremely effective in purifying diesel engine exhaust gas.

In general, the catalyst of the present invention also has excellent high-temperature surface durability, so it can be installed in a Tea Cell vehicle without causing any practical problems.

As described above, the catalyst of the present invention is extremely useful as a catalyst for purifying diesel engine exhaust gas.

(Examples) Hereinafter, the present invention will be roughly and specifically explained with reference to Examples.

In addition, the distribution shape of rhodium in the catalyst component supporting layer>y1
7 If you get stuck, use EPMA (Electron Probe).
Micr.

analyzer) (manufactured by Kinsei Seisakusho Co., Ltd.).

Example 1 1 kg of alumina with a specific surface area of 90 m2/g was added to an aqueous solution in which palladium nitrate (hereinafter referred to as 12.5 g of palladium nitrate (palladium equivalent)) containing 12.5 g of palladium was dissolved in deionized water. Pour in, stir thoroughly, and dry at 150°C for 3 hours.
The alumina-palladium powder is macerated by firing at 0℃ for 2 hours.
Ta.

This powder 11 (g) was wet-pulverized to form a slurry.

This slurry has a 5.66 inch diameter x 6.5 mm diameter oven cell with approximately 300 oven cells per square inch of cross section. After soaking a 0 inch long cylindrical cordierite honeycomb carrier and removing the excess slurry,
The alumina-palladium powder was dried at 150°C for 2 hours and then calcined at 500°C for 1 hour to obtain a
A structure carrying 1 g was obtained.

Next, 11<g of alumina with a specific surface area of 90 m/g was added to an aqueous solution containing 5 g of rhodium nitrate (rhodium equivalent) dissolved in deionized water, stirred thoroughly, and heated at 150°C.
The powder was dried at 500°C for 3 hours, and then fired at 500°C for 2 hours to obtain alumina-rhodium powder.

1 kg of this alumina-rhodium powder was wet-pulverized to form a slurry, and the above-mentioned alumina-palladium supporting structure was immersed, and after removing excess slurry, it was heated at 150°C for 30 minutes.
The catalyst was dried for an hour and then calcined at 500°C for an hour to obtain a catalyst in which 20.1 g of this alumina-rhodium powder was supported per structure IQ.

The supported amounts of alumina, palladium, and rhodium in this catalyst were 100 g, 1 g, and 0 g per structure 12.
．． It was 1g.

Further, rhodium was contained only in the upper layer portion having a thickness corresponding to 30% of the thickness of the catalyst component supporting layer.

Example 2 1 kg of alumina with a specific surface area of 150 m2/g was added to an aqueous solution in which 20 g of dinitrodiaminoplatinum (in terms of platinum) was dissolved in deionized water, stirred thoroughly, and heated at 150°C for 3 hours.
It was dried for an hour and then opened for 21 minutes at 500°C to obtain an alumina-platinum powder.

1 kg of this powder was wet-pulverized to form a slurry, and the same cordierite honeycomb carrier used in Example 1 was immersed in this slurry, and after removing excess slurry,
It was dried at 50°C for 2 hours and then fired at 500°C for 1 hour to obtain a structure in which 51 g of alumina-platinum powder was supported per 1 g of the structure.

Next, Ikg of alumina with a specific surface area of 90 m2/g was poured into an aqueous solution of 10 g of rhodium nitrate (rhodium equivalent) dissolved in deionized water, thoroughly stirred, dried at 150°C for 3 hours, and then heated to 500°C. The mixture was fired for 2 hours to obtain alumina-rhodium powder.

1 kg of this alumina-rhodium powder was wet-pulverized to form a slurry, the alumina platinum supporting structure was immersed in this slurry, excess slurry was removed, and the mixture was heated to 150°C.
dried for 3 hours, then baked at 500°C for 1 hour,
A catalyst was obtained in which 50.5 g of alumina-platinum powder was supported per 1Ω of the structure.

The supported amounts of alumina, platinum, and rhodium in this catalyst were 100 g-1 g and 0.5 g, respectively, per 1 g of the structure.

Further, rhodium was contained only in the northern layer portion whose thickness corresponded to 60% of the thickness of the catalyst component supporting layer.

Example 3 11 kg of alumina with a specific surface area of 150 m2/g was charged into an aqueous solution ζ in which 16.7 g of palladium nitrate (in terms of palladium) and 8.3 g of chloroplatinic acid (rF- in terms of platinum) were dissolved in deionized water. After stirring, the mixture was dried at 150°C for 3 hours and then calcined at 750'C for 1 hour to obtain alumina-palladium-platinum powder.

1 kg of this powder was wet-pulverized into a slurry, and the same cordierite honeycomb carrier used in Example 1 was immersed in the slurry, and the excess slurry was removed.
The alumina palladium-platinum powder was dried for 2 hours at 150°C, then fired at 500°C for 1 hour.
A structure was obtained in which 62 g was supported per 2 pieces.

Next, 1 kg of alumina with a specific surface area of 120 m2/g
was added to an aqueous solution of 12.5 g (rhodium equivalent) of hexaammine rhodium chloride dissolved in deionized water,
After thorough stirring, the mixture was dried at 180'C for 3 hours, and then calcined at 500C for 1 hour to obtain alumina-rhodium powder. 1 kg of this alumina-rhodium powder was wet-pulverized to form a slurry, and the above-mentioned alumina-palladium-platinum supporting structure was immersed in this slurry, and after removing excess slurry, it was dried at 150°C for 2 hours, and then '
The structure was calcined for 1 hour at C and tH to support 40.5 g of alumina-rhodium powder per 1 g of the structure.

The amount of alumina, palladium, platinum and rhodium supported in this catalyst is 100g each per 1g of structure.
, 1g, 0.5g and 0.5g tea.

In addition, rhodium is contained only in the layer portion with a thickness corresponding to 50% of the thickness of the catalyst component supporting layer. was added to an aqueous solution of deionized water, thoroughly stirred, dried at 150°C for 6 hours, and then calcined at 700°C for 1 hour to obtain zirconia-palladium powder.

1 kg of this powder was wet-pulverized to form a slurry, and this slurry was immersed in the same caushlite honeycomb carrier used in Example 1. After removing excess slurry,
The zirconia-palladium powder was dried at 50°C for 3 hours, blown and fired at 500°C for 1 hour to form a powder of zirconia-palladium powder of 50% per 12 structures.
A structure carrying 1 g was obtained.

Next, zirconia IJ with a specific surface area of 80rn2/g<
g was added to an aqueous solution of 20 g of rhodium nitrate (rhodium equivalent) dissolved in deionized water, and after stirring thoroughly,
It was dried at 0°C for 3 hours and then fired at 500°C for 1 hour to obtain a zirconia-rhodium powder.

This zirconia-rhodium powder was wet-pulverized to form a slurry, and the zirconia-palladium supporting structure was immersed in this slurry, and after removing excess slurry,
The zirconia-rhodium powder was dried at 0°C for 2 hours and then fired at 700°C for 2 hours to obtain a powder of zirconia-rhodium powder of 5.1
A supported catalyst was obtained.

The amounts of zirconia, palladium and rhodium supported on this catalyst were 55 g, Ig and 0.1 g, respectively, per 12 structures.

Further, rhodium was contained only in the upper layer portion having a thickness corresponding to 20% of the thickness of the catalyst component supporting layer.

Example 5 Zirconia 11 (g) with a specific surface area of 60 m2/g was poured into an aqueous solution in which 25 g of palladium chloride (palladium equivalent) and 165 g of praseodymium nitrate were dissolved in deionized water.
After stirring thoroughly, dry at 150'C for 6 hours.
The powder was calcined at 00'C for 2 hours to obtain alumina-palladium-praseodymium oxide powder.

1 kg of this powder is wet-milled into a slurry, and this slurry is made into a 5° 66 inch diameter x 6.
After soaking an inch-long cylindrical stainless steel honeycomb carrier and removing excess slurry, it was dried at 180°C for 2 hours, and then calcined at 650°C for 3 hours to remove the alumina.
Palladium-praseodymium oxide powder per gram of structure
A structure carrying 7g was obtained.

Next, 1 kg of zirconia with a specific surface area of 90 m2/g,
5 g of rhodium nitrate (rhodium equivalent) was added to an aqueous solution of deionized water, thoroughly stirred, dried at 1508 C for 3 hours, and then calcined at 500 C for 2 hours to obtain Silconia Rhosi J1 powder. Ta.

1 kg of this powder was wet-pulverized to form a slurry, the above parasicum praseodymium oxide supporting structure was immersed in the slurry, and the excess slurry was removed.], 50
The zirconia-rhodium powder was dried at 400°C for 6 hours and then fired at 400°C for 1 hour to form a zirconia-rhodium powder of 20
．． 1g of supported catalyst was obtained.

The supported amounts of zirconia, palladium, rhodium, and praseodymium oxide in this catalyst were 100 g, 2 g, 0.1 g, and 5 g, respectively, per 1 g of the structure.

Further, rhodium was contained only in the upper layer portion having a thickness corresponding to 30% of the thickness of the catalyst component supporting layer.

Example 6 I kg of alumina with a specific surface area of 150 m"/g was mixed with 20 g of dinitrodiaminoplatinum (in terms of platinum) and 1 kg of cerium nitrate.
510g was added to an aqueous solution dissolved in deionized water, thoroughly stirred, and then dried at 150°C for 6 hours.
It was calcined for 2 hours at ℃ to obtain an alumina-platinum-sevenia powder.

1 kg of this powder is wet-milled to form a slurry, and this slurry is made into a 5° 66 inch diameter x 6.
A cylindrical honeycomb carrier of 0 inch length was soaked at 150°C after removing excess slurry.
The structure was then dried at 400 DEG C. for 2 hours to obtain a structure in which 81 g of alumina and gold ceria powder was supported per structure IQ.

Next, 1 kg of alumina with a specific surface area of 150 m2/g,
5 g of rhodium nitrate (rhodium equivalent) and 266 g of lanthanum nitrate were dissolved in deionized water, stirred thoroughly, and then dried at 150°C for 3 hours.
The mixture was fired at 0°C for 1 hour to obtain alumina-〇dium-lanthanum oxide powder.

This Klkg was wet-pulverized to form a slurry, and the alumina-platinum-septalia support structure was immersed in this slurry, excess slurry was removed, and then dried at 150°C for 3 hours. After firing at 600°C for 1 hour, the alumina-rhodium-lanthanum oxide powder was produced at 1 per structure IQ.
10.5g of supported catalyst was obtained.

In this catalyst, the supported amounts of alumina, platinum, rhodium, ceria, and lanthanum oxide were 150 g, 1 g, 0.5 g, 30 g, and 10 g per structure 12, respectively.

Further, rhodium was contained only in the upper layer portion, which corresponded to 70% of the thickness of the catalyst component supporting layer.

Example 7 1 kg of silica with a specific surface area of 55 m2/g was added to an aqueous solution in which 20 g of palladium chloride (in terms of palladium) and 6 g of chloroplatinic acid (in terms of platinum) were dissolved in deionized water, stirred thoroughly, and then heated at 150°C. Dry for 3 hours, then 60
The mixture was calcined at 0°C for 2 hours to obtain silica-palladium-platinum powder.

1 kg of this powder was wet-pulverized to form a slurry, and the same stainless steel honeycomb carrier as used in Example 5 was immersed in this slurry, and after removing excess slurry,
The silica-palladium platinum powder was dried at 0°C for 3 hours and then calcined at 500°C for 1 hour to obtain a
．． A structure carrying 3 was obtained.

Next, 11 g of titania with a specific surface area of 65 rn2/g was added to an aqueous solution containing 50 g of rhodium nitrate (rhodium equivalent) dissolved in deionized water, stirred thoroughly, and heated to 150°
The titania-rhodium powder was dried at 400°C for 3 hours and then fired at 400°C for 1 hour.

This powder 11 (g) was wet-pulverized to form a slurry, the upper layer silica palladium-platinum supporting structure was immersed in this slurry, and the excess slurry was removed.
After drying for a period of time, the structure was then calcined at 500° C. for 1 hour to obtain a catalyst in which 10.5 g of natania arosium powder was supported per 1 g of the structure.

The supported amounts of silica, titania, palladium, platinum, and rhodium in this catalyst were 50 g, 10 g, Ig, 0.3 g, and 0.5 g per 12 structures, respectively.

Further, rhodium was contained only in the upper layer portion having a thickness corresponding to 25% of the thickness of the catalyst component supporting layer.

Example 8 1 kg of alumina with a specific surface area of 150 m2/g was poured into an aqueous solution in which 25 g of baracium sulfite complex salt (in terms of palladium) and 12.5 g of platinum sulfite complex salt (in terms of platinum) were dissolved in deionized water. After stirring, 150
It was dried at 800°C for 3 hours and then fired at 800°C for 5 hours to obtain alumina-palladium-platinum powder.

This powder 11 (g) was wet-pulverized to form a slurry, and the same Kosierai I-made Honey 11 carrier used in Example 1 was immersed in the slurry, and after removing the excess slurry, the mixture was heated at 150°C for 6 hours. Structure 1
A structure carrying 4.1.5 g/g was obtained.

Next, 1 kg of zirconia with a specific surface area of 40 m2/g,
dinitrodiamycin,) 8.3 g of platinum (1 quadrant of platinum) and 8.3 g of rhodium nitrate (converted to rhodium) were dissolved in deionized water.
It was dried at 0°C for 6 hours and then fired at 750°C for 4 hours to obtain zirconia-platinum-rhodium powder.

This powder 11 (g) was wet-pulverized to form a slurry, the alumina-palladium-platinum supporting structure was immersed in this slurry, excess slurry was removed, and the mixture was heated at 150°C for 30 minutes.
The zirconia-palladium-platinum powder was dried for 2 hours at 400°C and then baked at 400°C for 61.0 hours per gram of the structure.
A supported catalyst was obtained.

The amount of alumina, zirconia, palladium, platinum, and Rossiu J1 supported in this catalyst is 1! 40g, 60g, Ig, Ig and 0.5g per II, respectively.

Further, rhodium was contained only in the upper layer portion, which corresponded to 70% of the thickness of the catalyst component supporting layer.

Example 9 1 kg of alumina having a specific surface area of 150 m2/g was weighed and wet-pulverized with water to form a slurry. This slurry has a 5.66 inch diameter x 6.5 mm diameter with approximately 400 open flow gas flow cells per square inch of cross section. A cylindrical cordierite honeycomb carrier with a length of OO inches was immersed, excess slurry was removed, and then dried at 150°C for 3 hours.
Next, it was fired at 500°C for 1 hour to obtain a structure supporting alumina.

This structure is 80° containing 0.4g of rhodium.
It was immersed in a rhodium nitrate aqueous solution 2.5Q of C to adsorb rhodium, and after removing the excess solution, it was dried at 150°C for 3 hours, and then calcined at 700°C for 1 hour to transfer rhodium onto the alumina support structure. It was carried by

Next, 3.8 g of salt-milled auric acid (in terms of platinum) and 38.5 g of palladium chloride (in terms of palladium) were added to deionized water ζ
The upper layer alumina rhodium supporting structure was immersed in an aqueous solution containing 2.5% of this solution, and after removing excess solution, 150% of the aqueous solution was dissolved.
The catalyst was dried at 500°C for 3 hours and then calcined at 500°C for 2 hours.

The supported amounts of alumina, palladium, platinum, and rhodium in this catalyst are 50 g, 2 g, and 0 g per 1 g of the structure.
．． 2g and 0.2g.

Further, rhodium was contained only in the upper layer portion having a thickness corresponding to 20% of the thickness of the catalyst component supporting layer.

Example 10 Ceramic skeleton formed with a cell count of about 12 per inch and a porosity of about 90% 5.66 inch diameter x 6.00 inch length A catalyst was obtained in the same manner as in Example 4, except that a cylindrical cordierite ceramic foam was used.

The supported amounts of zirconia, palladium, and rhodium in this catalyst are 55 g and 1 g, respectively, per Ig of structure.
and 0.1 g.

Further, rhodium was contained only in the upper layer portion having a thickness corresponding to 20% of the thickness of the catalyst component supporting layer.

Comparative Example 1 Ikg of alumina with a specific surface area of 150 m2/g was poured into an aqueous solution in which 10 g of palladium nitrate (in terms of palladium) was dissolved in deionized water, stirred thoroughly, and dried at 150°C for 3 hours. , - and calcined for 1 hour to obtain alumina-palladium powder.

1 kg of this powder was wet-pulverized to form a slurry. A honeycomb carrier manufactured by Corzierai (.
The catalyst was dried at 50°C for 3 hours and then calcined at 500°C for 1 hour.

The amounts of alumina and palladium supported in this catalyst were 100 g and 1 g, respectively, per Ig of structure.

Comparative Example 2 A catalyst was obtained in the same manner as in Comparative Example 1 except that dinitroaminoplatinum was used instead of palladium nitrate.

The supported amounts of alumina and platinum in this catalyst were 100 g and 1 g, respectively, per 1 g of the structure.

Comparative Example 3 1 kg of alumina with a specific surface area J50rrr2/g was added to an aqueous solution in which 10 g of palladium nitrate (palladium equivalent) and chloroplatinic acid 10 g (platinum equivalent) were dissolved in deionized water, stirred thoroughly, and heated to 150°C for 30 minutes. The alumina-palladium-
A platinum powder was obtained.

Thereafter, a catalyst was obtained in the same manner as in Comparative Example 1.

The supported amounts of alumina, palladium, and platinum in this catalyst were 100 g, Ig, and 1 g, respectively, per Ig of the structure.

Comparative Example 4 I kg of alumina with a specific surface area of 90 m2/g was mixed with 10 g of palladium nitrate (palladium equivalent) and 0.0 g of rhodium nitrate.
1 g (TFF dium equivalent) was added to an aqueous solution dissolved in deionized water, thoroughly stirred, dried at 150°C for 3 hours, and then calcined at 500°C for 2 hours to form alumina-palladium-rhodium powder. I got it.

Thereafter, a catalyst was obtained in the same manner as in Comparative Example 1.

The supported amounts of alumina, palladium, and rhodium in this catalyst are 100 g each per 1 g of the structure, and Ig
and 0.1 g.

Comparative Example 5 1 kg of alumina with a specific surface area of 150 m2/g was added to an aqueous solution containing 10 g of dinitrodiaminoplatinum (in terms of platinum) and 5 g of rhodium nitrate (in terms of rhodium) dissolved in deionized water, stirred thoroughly, and then heated at 150°C. It was dried for 3 hours and then calcined at 500°C for 1 hour to obtain alumina-platinum-rhodium powder.

Thereafter, a catalyst was obtained in the same manner as in Comparative Example 1.

The supported amounts of alumina, platinum, and rhodium in this catalyst were 100 g, 1 g, and 0 g, respectively, per Ig of the structure.
．． It was 5g.

Comparative Example 6 1 kg of alumina with a specific surface area of 150 m2/g was mixed with 10 g of palladium nitrate (in terms of palladium), 5 g of chloroplatinic acid (in terms of platinum), and 5 g of hegizaammine rhodium chlorite.
(rhodium equivalent) was added to an aqueous solution of deionized water, stirred thoroughly, and dried at 150°C for 3 hours. A powder was obtained.

Thereafter, a catalyst was obtained in the same manner as in Comparative Example 1.

The amount of alumina, palladium, platinum and rhodium supported in this catalyst is 100g each per 1g of structure.
, Ig, 0.5 g and 0.5 g.

Table 1 summarizes the supported amounts of each component in the catalysts obtained in Examples 1 to 11 and Comparative Examples 1 to 6, and the ratio of the upper layer where rhodium exists to the catalyst component supported layer.
Shown below. (Left below) Reference Examples The diesel engine exhaust gas purification performance of the catalysts obtained in Examples 1 to 10 and Comparative Examples 1 to 6 was evaluated.

Supercharged direct injection day cell engine (4 cylinders, 2800cc
) and light oil with a sulfur content of 0.47% by weight as fuel.

Each catalyst is installed in the exhaust gas pipe from the upper engine, and the engine speed is 250. A 300 hour durability test was conducted under the conditions of full ORPM load and catalyst inlet temperature of 600°C.

After that, the engine speed is 2000 rpm,) Luk 8.5
kg-m and the catalyst inlet temperature of 300 °C, the content of particulate matter in the exhaust gas before entering the catalyst bed (population) and after leaving the catalyst bed (outlet) is determined by conventional dilution]. The degree of removal of particulate matter, that is, the purification rate (%), was determined using the tunnel method. In addition, sulfur dioxide, gaseous hydrocarbons, and carbon monoxide in the exhaust gas before entering the catalyst bed and in the exhaust gas after passing through the catalyst bed were analyzed at the same time to determine the conversion rate.

The results are shown in Table 2. (Margin below)

Claims (6)

[Claims] (1) At least one selected from (a) refractory inorganic oxide, (b) palladium and platinum
A diesel engine exhaust gas purification catalyst in which a catalyst component containing various noble metals and (c) rhodium is supported on a refractory three-dimensional structure, the thickness being equivalent to 80% or less of the thickness of the catalyst component supporting layer. A diesel engine exhaust gas purification catalyst characterized by containing rhodium only in the upper layer. (2) The catalyst component supporting layer consists of two layers, and the first layer in contact with the refractory three-dimensional structure is made of (a) a refractory inorganic oxide, and (b) at least one layer selected from palladium and platinum.
catalytic component containing the above-mentioned noble metal;
The catalyst for purifying diesel engine exhaust gas according to claim 1, wherein the second layer on the layer comprises a catalyst component containing (a) a refractory inorganic oxide and (c) rhodium. (3) At least the refractory inorganic oxide is selected from the group consisting of activated alumina, silica, titania, zirconia, silica-alumina, alumina-zirconia, alumina-titania, silica-titania, silica-zirconia, titania-zirconia, and zeolite. The catalyst for purifying diesel engine exhaust gas according to claim 1, which is one type of catalyst. (4) Claim (1) wherein the refractory inorganic oxide is zirconia.
) The catalyst for purifying diesel engine exhaust gas described in ). (5) Claim (1) wherein the fire-resistant three-dimensional structure is a ceramic foam, an open-flow ceramic honeycomb, a wall-flow type honeycomb monolith, an open-flow metal honeycomb, a metal foam, or a metal mesh.
) The diesel engine exhaust gas purification catalyst described in ). (6) The diesel engine exhaust gas catalyst according to claim 1, wherein the refractory three-dimensional structure is an open-flow ceramic honeycomb or an open-flow metal honeycomb.